Tranilast, (2-[[3-(3,4-dimethoxyphenyl)-1-oxo-2-propenyl]amino]benzoic acid), shown below, is a therapeutic agent that exhibits an anti-allergic effect. It has been shown to inhibit the release of inflammatory mediators, such as histamine, from mast cells and basophils (P. Zampini. Int J Immunopharmacol. 1983; 5(5): 431-5). Tranilast has been used as an anti-allergic treatment, for several years in Japan and South Korea, for conditions such as allergic conjunctivitis, bronchial asthma, allergic rhinitis and atopic dermatitis.

Tranilast is currently marketed in Japan and South Korea by Kissei Pharmaceutical Co. Ltd under the Rizaben® brand name. As well as displaying an anti-allergic effect tranilast has been shown to possess anti-proliferative properties. Tranilast was found to inhibit the proliferation of fibroblasts and suppress collagen synthesis (M. Isaji. Biochem Pharmacol. 1987; 36: 469-474) and also to inhibit the transformation of fibroblasts to myofibroblasts and their subsequent contraction (M. Isaji. Life Sci. 1994; 55: 287-292). On the basis of these effects tranilast is now also indicated for the treatment of keloids and hypertrophic scars. Its anti-fibrotic action is believed to be due to its ability to inhibit transforming growth factor beta (TGF-β) (H. Suzawa. Jpn J Pharmacol. 1992 October; 60(2): 91-96). TGF-β induced fibroblast proliferation, differentiation and collagen synthesis are known to be key factors in the progression of idiopathic pulmonary fibrosis and tranilast has been shown in-vivo to have potential in the treatment of this chronic lung disease (T. Jiang. Afr J Pharm Pharmaco. 2011; 5(10): 1315-1320). Tranilast has also been shown in-vivo to be have potential beneficial effects in the treatment of airway remodelling associated with chronic asthma (S. C. Kim. J Asthma. 2009; 46(9): 884-894.
It has been reported that tranilast also has activity as an angiogenesis inhibitor (M. Isaji. Br J Pharmacol. 1997; 122(6): 1061-1066). The results of this study suggested that tranilast may be beneficial for the treatment of angiogenic diseases such as diabetic retinopathy and age related macular degeneration. As well as showing inhibitory effects on mast cells and fibroblasts, tranilast has also demonstrated an ability to diminish tumor necrosis factor-alpha (TNF-α) from cultured macrophages (H. O. Pae. Biochem Biophys Res Commun. 371: 361-365) and T-cells (M. Platten. Science. 310: 850-855), and inhibited NF-kB-dependent transcriptional activation in endothelial cells (M. Spieker. Mol Pharmacol. 62: 856-863). Recent studies have revealed that tranilast attenuates inflammation and inhibits bone destruction in collagen induced arthritis in mice suggesting the possible usefulness of tranilast in the treatment of inflammatory conditions such as arthritis (N. Shiota. Br J Pharmacol. 2010; 159 (3): 626-635).
As has recently been demonstrated, in-vitro and in-vivo, tranilast also possesses an anti-tumor action. Tranilast has been shown to inhibit the proliferation, apoptosis and migration of several cell lines including breast cancer (R. Chakrabarti. Anticancer Drugs. 2009 June; 20(5): 334-45) and prostate cancer (S. Sato. Prostate. 2010 February; 70(3): 229-38) cell lines. In a study of mammary carcinoma in mice tranilast was found to produce a significant reduction in metastasis (R. Chakrabarti. Anticancer Drugs. 2009 June; 20(5): 334-45). In a pilot study in humans, tranilast was shown to have the potential to improve the prognosis of patients with advanced castration-resistant prostate cancer (K. Izumi. Anticancer Research. 2010 July; 30: 73077-81).
It has been reported that tranilast has the ability to induce or enhance neurogenesis and, therefore, could be used as an agent to treat neuronal conditions such as cerebral ischemia, glaucoma, multiple sclerosis, amyotrophic lateral sclerosis, Alzheimer's disease, neurodegenerative trinucleotide repeat disorders, neurodegenerative lysosomal storage diseases, spinal cord injury and trauma, dementia, schizophrenia and peripheral neuropathy (A. Schneider. EP2030617).
Tranilast's beneficial properties have been reported to have utility in several ocular conditions. Tranilast is currently approved in Japan and Korea for the treatment of allergic conjunctivitis. WO2010137681 claims the use of tranilast as a prophylactic or therapeutic agent for the treatment of retinal diseases. The anti-fibrotic properties of tranilast have been reported to be of benefit in maintaining the filtering blob during glaucoma surgery and this has been demonstrated in a pilot study in humans (E. Chihara. J Glaucoma. 1999; 11(2): 127-133). There have also been several reported cases of the beneficial use of tranilast in the prevention of postoperative recurrence of pterygium (C. Fukui. Jap J Opthalmol. 1999; 12: 547-549). Tsuji recently reported that tranilast may be beneficial not only in the prevention of pterygium recurrence, but also for the inhibition of symblepharon and granuloma formation (A. Tsuji. Tokai J Exp Clin Med. 2011; 36(4): 120-123). Collectively it has been demonstrated that tranilast possesses anti-allergic, anti-fibrotic, anti-inflammatory, anti-tumor, neurogenesis enhancing and angiogenesis inhibitory properties and as such may be useful for the treatment of diseases associated with such properties.
Tranilast occurs as a yellow crystalline powder that is identified by CAS Registry Number: 53902-12-8. As is typical of cinnamic acid derivatives (G. M. J. Schmidt J. Chem. Soc. 1964: 2000) tranilast is photochemically unstable when in solution, transforming into cis-isomer and dimer forms on exposure to light (N. Hori. Cehm Pharm Bull. 1999; 47: 1713-1716). Although pure crystalline tranilast is photochemically stable in the solid state it is practically insoluble in water (14.5 μg/ml) and acidic media (0.7 μg/ml in pH 1.2 buffer solution) (Society of Japanese Pharmacopoeia. 2002). Although tranilast has shown activity in various indications, it is possible that the therapeutic potential of the drug is currently limited by its poor solubility and photostability. High energy amorphous forms are often used as a means of improving the solubility of poorly soluble APIs, however, literature shows that amorphous solid dispersions of tranilast are not completely photostable in the solid state and that they undergo photodegradation on storage when exposed to light (S. Onoue. Eur J Pharm Sci. 2010; 39: 256-262). US20110136835 describes a combination of tranilast and allopurinol and its use in the treatment of hyperuricemia associated with gout and has one mention of a “co-crystal form”, but lacks any further description or characterization.
There is a need therefore to develop tranilast compositions that have improved solubility and/or photostability. A new tranilast composition and/or cocrystal of the invention answers one or both of these needs. A new tranilast composition and/or cocrystal of the invention may have other beneficial properties such as increased solubility, improved dissolution, and/or increased bioavailability when compared to tranilast itself.
Although therapeutic efficacy is the primary concern for an active pharmaceutical ingredient (API), the chemical composition and solid state form (i.e., the crystalline or amorphous form) of the API can be critical to its pharmacological properties, such as bioavailability, and to its development as a viable drug candidate. Compositions and crystalline forms of some API's have been used to alter the API's physicochemical properties. Each composition or crystalline form can have different solid state (physical and chemical) properties. The differences in physical properties exhibited by a novel solid state forms (such as, for example, a polymorph of the API or a cocrystal containing the API, discussed below) may affect pharmaceutical and pharmacological properties such as storage stability, compressibility and density (important in formulation and product manufacturing), and/or solubility and dissolution rates (important factors in determining bioavailability). For example, the rate of dissolution of an active ingredient in a patient's stomach fluid may have therapeutic consequences since it impacts the rate at which an orally administered active ingredient may reach the patient's bloodstream. Because these practical properties are influenced by the solid state properties, e.g. the crystalline form of the API, they can impact the selection of a particular compound as an API, the ultimate pharmaceutical dosage form, the optimization of manufacturing processes, and absorption in the body.
Physical properties of an API also have a major influence on the ability to deliver a drug by a desired method. For example, if a drug is delivered by inhalation physical properties relating to the API as a particle, such as morphology, density, surface energy, charge, hygroscopicity, stability, dispersive properties and/or agglomeration, can come into play. The solid state form of the API, and as described below, cocrystals of the API, provide opportunities to address, engineer and/or improve upon one or more of such properties and thereby upon methods of delivery.
Obtaining crystalline forms of an API, when possible, is also extremely useful in drug development. It permits better characterization of the drug candidate's chemical and physical properties. Crystalline forms often have better chemical and physical properties than the API in its amorphous state. Moreover, finding the most adequate solid-state form for further drug development can reduce the time and the cost of that development.
It may be possible to achieve more desirable properties of a particular API by forming a cocrystal of the API. A cocrystal of an API is a distinct chemical composition of the API and coformer(s) and generally possesses distinct crystallographic and spectroscopic properties when compared to those of the API and coformer(s) individually. Crystallographic and spectroscopic properties of crystalline forms are typically measured by X-ray powder diffraction (XRPD) and single crystal X-ray crystallography, among other techniques. Cocrystals often also exhibit distinct thermal behavior. Thermal behavior is measured in the laboratory by such techniques as capillary melting point, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). As crystalline forms, cocrystals may possess more favorable solid state, physical, chemical, pharmaceutical and/or pharmacological properties or be easier to process than known forms or formulations of the API. For example, a cocrystal may have different dissolution and/or solubility properties than the API and can therefore be more effective in therapeutic delivery. New pharmaceutical compositions comprising a cocrystal of a given API may therefore have different or superior properties as compared to its existing drug formulations.